Electric circuit management method and device

Abstract

The invention proposes a method of managing an electronic circuit of the type comprising a memory (EEPROM) for the storage of confidential information, the method comprising masking variations of the electrical current (I) consumed by the electronic circuit, during a fraction of the time only (t i -t j ), at least during the portion(s) of time during which an instruction bearing on confidential data is executed, and notably an instruction for reading out from the memory (EEPROM).

1. A method for controlling an electronic circuit, said method comprising the steps of:
 executing instructions, at least one of the instructions operating on confidential data; 
 masking variations in the current consumed by the electronic circuit by keeping the current consumed by the electronic circuit substantially constant during only a portion of the operating time of the electronic circuit, which at least includes the time during which the instruction operating on confidential data is executed but does not include the entire operating time of the electronic circuit; 
 activating a circuit for masking variations in the current consumed by the electronic circuit by executing of a first instruction; and 
 deactivating the circuit for masking variations in the current consumed by the electronic circuit by executing a second instruction, 
 wherein the first instruction is executed some time before the instruction operating on confidential data is executed, and the second instruction is executed some time after the instruction operating on confidential data is executed. 
 
   
   
     2. The method as defined in  claim 1 , wherein the portion of the operating time during which variations in the current consumed by the electronic circuit are masked includes the time during which an instruction for reading from a memory containing confidential data is executed. 
   
   
     3. The method as defined in  claim 1 , wherein the first instruction causes a predetermined logic value to be written in a register of the electronic circuit, and the second instruction causes a complementary logic value to be written in the register. 
   
   
     4. A tangible computer-readable medium encoded with a program for controlling an electronic circuit, said program containing instructions for performing the steps of:
 operating on non-confidential data; 
 operating on confidential data; 
 masking variations in the current consumed by the electronic circuit by keeping the current consumed by the electronic circuit substantially constant during only a portion of the operating time of the electronic circuit, which at least includes the time during which the confidential data is operated on but does not include the entire operating time of the electronic circuit; 
 activating a circuit for masking variations in the current consumed by the electronic circuit through a first instruction; and 
 deactivating the circuit for masking variations in the current consumed by the electronic circuit through a second instruction, 
 wherein the first instruction is executed some time before the confidential data is operated on, and the second instruction is executed some time after the confidential data is operated on. 
 
   
   
     5. The tangible computer-readable medium as defined in  claim 4 , wherein the portion of the operating time during which variations in the current consumed by the electronic circuit are masked includes the time during which a read from a memory containing confidential data is performed. 
   
   
     6. The tangible computer-readable medium as defined in  claim 4 , wherein the first instruction causes a predetermined logic value to be written in a register of the electronic circuit, and the second instruction causes a complementary logic value to be written in the register. 
   
   
     7. An electronic circuit having a memory for storing confidential information, said electronic circuit comprising:
 a masking circuit for masking variations in the electrical current consumed by the electronic circuit by keeping the current consumed by the electronic circuit substantially constant during only a portion of the operating time of the electronic circuit, which at least includes the time during which an instruction operating on confidential data is executed but does not include the entire operating time of the electronic circuit; and 
 a selection circuit for selectively activating and deactivating the masking circuit, the selection circuit activating the masking circuit when a first instruction is executed, and deactivating the masking circuit when a second instruction is executed, 
 wherein the first instruction is executed some time before the instruction operating on confidential data is executed, and the second instruction is executed some time after the instruction operating on confidential data is executed. 
 
   
   
     8. The electronic circuit as defined in  claim 7 , further comprising a register coupled to the selection circuit, the selection circuit activating or deactivating the masking circuit in accordance with a logic value stored in the register. 
   
   
     9. The electronic circuit as defined in  claim 8 , further comprising: a central processing unit; a first read-only memory for storing a control program for execution by the central processing unit; and a second read-only memory for storing the confidential information. 
   
   
     10. The electronic circuit as defined in  claim 9 , wherein the control program includes: the first instruction which causes a predetermined logic value to be written into the register, and
 the second instruction which causes a complementary logic value to be written in the register. 
 
   
   
     11. The electronic circuit as defined in  claim 10 , wherein the control program further includes a third instruction which is the instruction operating on the confidential information, and in the control program, the first instruction is before the third instruction, and the second instruction is after the third instruction. 
   
   
     12. The electronic circuit as defined in  claim 11 , wherein the third instruction causes the confidential information to be read from the second read-only memory. 
   
   
     13. An information processing system including at least one electronic circuit having a memory for storing confidential information, said electronic circuit comprising:
 a masking circuit for masking variations in the electrical current consumed by the electronic circuit by keeping the current consumed by the electronic circuit substantially constant during only a portion of the operating time of the electronic circuit, which at least includes the time during which an instruction operating on confidential data is executed but does not include the entire operating time of the electronic circuit; and 
 a selection circuit for selectively activating and deactivating the masking circuit, the selection circuit activating the masking circuit when a first instruction is executed, and deactivating the masking circuit when a second instruction is executed, 
 wherein the first instruction is executed some time before the instruction operating on confidential data is executed, and the second instruction is executed some time after the instruction operating on confidential data is executed. 
 
   
   
     14. The information processing system as defined in  claim 13 , wherein the electronic circuit further comprises a register coupled to the selection circuit, the selection circuit activating or deactivating the masking circuit in accordance with the logic value stored in the register. 
   
   
     15. The information processing system as defined in  claim 14 , wherein the electronic circuit further comprises:
 a central processing unit; 
 a first read-only memory for storing a control program for execution by the central processing unit; and a second read-only memory for storing the confidential information. 
 
   
   
     16. The information processing system as defined in  claim 15 , wherein the control program includes the first instruction which causes a predetermined logic value to be written into the register, the second instruction which causes a complementary logic value to be written in the register, and a third instruction which is the instruction operating on the confidential information, and
 in the control program, the first instruction is before the third instruction, and the second instruction is after the third instruction.